Back-scattering technique is one of the techniques for human body inspection. It scans a human body with beams of X-rays, and receives scattered signals by a large-area detector at the same time. A scattering image of the human body can be obtained through data processing which maps scanning locations to scattered signals.
In the case where a back-scattering device and a human to be scanned both are stationary, one-time scanning can only scan and obtain an image of one side of the human. If a complete inspection is to be performed on the human, the human needs to turn around after scanning of one side, so as to scan the other side.
In order to enhance the efficiency of security inspection, several manufacturers adopted a solution in their back-scattering security inspection systems, in which two back-scattering devices are placed in opposite positions relative to each other so that a human to be scanned stands therebetween when the human is to be scanned. The two back-scattering devices each scan one side of the human body, and thereby there is no need for the human to turn around.
In the case that two devices are placed in opposite positions relative to each other, the two devices typically will not emit beams at the same time. The reason is that if one device emits when the other one is emitting, the one device generates signals on the detector of the other one and thus the scanning image cannot be obtained correctly. Therefore, in the system where two devices stand and scan oppositely, the ray sources in the two devices emit beams in a time-sharing manner, as described in for example Patent Document 1 (CN1019818820A). Thus, a back-scattering system that utilizes time-sharing emission has scanning time that is not less than double of the scanning time of one device.